Graphitization Temperature Research Articles

PEFC Electrocatalysts using Highly-Graphitized Mesoporous Carbon Supports

The electrocatalysts used in polymer electrolyte fuel cells (PEFCs) are subject to oxidative corrosion of the carbon catalyst support due to start-stop cycling, as well as aggregation of Pt nanoparticles due to load fluctuations. The use of mesoporous carbon (MC) as a catalyst support has previously been shown to suppress aggregation. In this study, highly graphitized MC is prepared as a catalyst support to suppress both carbon corrosion and aggregation in Pt/MC electrocatalysts. The effect of graphitization temperature on the catalytic performance is evaluated, as well as the effect of pretreatment via either ball milling or pulverization to achieve suitable particle size. The results indicate that the initial activity of the electrocatalysts is improved by graphitization of the MC support after milling, and that the graphitization step improves the start-stop cycle durability.

Fabrication of high-performance graphene fiber: Structural evolution strategy from a two-step green reduction method

Graphene fibers (GFs) have a bright future in a variety of applications ascribing to their excellent performance. However, strict preparation conditions with extremely high graphitization temperature or toxic chemical reagents severely restrict their extensive implementation. Meanwhile, researchers are seeking easily scalable and eco-friendly GFs production methods. Here, we propose a green two-step reduction strategy involving L-ascorbic acid (LAA) chemical reduction followed by low-temperature annealing for the preparation of high-performance GFs. Benefiting from the elimination of macro-, micro- and nano-scaled defects and recombination of graphene nanosheets, the prepared GFs demonstrated amazing tensile strength of 778.49 MPa, Young's modulus of 92.61 GPa and an outstanding electrical conductivity of 3.2 × 104 S m−1, outperforming most of the chemically reduced GFs. This two-step green reduction strategy provides a new insight for constructing integrated high-performance GFs for sustainable application in many fields.

Low-Temperature Annealing of Nanoscale Defects in Polycrystalline Graphite

Polycrystalline graphite contains multi-scale defects, which are difficult to anneal thermally because of the extremely high temperatures involved in the manufacturing process. In this study, we demonstrate annealing of nuclear graphite NBG-18 at temperatures below 28 °C, exploiting the electron wind force, a non-thermal stimulus. High current density pulses were passed through the specimens with a very low-duty cycle so that the electron momentum could mobilize the defects without heating the specimen. The effectiveness of this technique is presented with a significant decrease in electrical resistivity, defect counts from X-ray computed tomography, Raman spectroscopy, and nanoindentation-based mechanical characterization. Such multi-modal evidence highlights the feasibility of nanoscale defect control at temperatures about two orders of magnitude below the graphitization temperature.

Sensitivity analysis and fuel performance of a control rod withdrawal in the generic fluoride-salt-cooled high temperature reactor

The purpose of this study is to develop boundary conditions with respect to input parameter uncertainty for fuel performance assessment of a control rod withdrawal transient in a fluoride-salt-cooled high-temperature reactor (FHR). Sensitivity analysis was performed to determine how certain key input parameters impacted the uncertainty of the outputs needed for the boundary conditions. The generated boundary conditions can be used in fuel performance codes to obtain failure probabilities and fuel performance envelopes. To accomplish this, we utilized a KP-AGREE model of the generic fluoride-salt-cooled high-temperature reactor (gFHR) and a pebble bed benchmark developed by Kairos Power. The key boundary conditions that were developed included the total power, maximum fuel region temperature, maximum fuel kernel temperature, and maximum moderator (graphite) temperature within the core. The sensitivity analysis was run until the Sobol indices and output converged within a 95 % confidence level; it was found that the coolant inlet temperature consistently had the highest impact on the uncertainty of the key core temperature values. The maximum bound of these temperatures also did not exceed 1123.5 °C for the fuel kernel and 973.7 °C for the moderator after the transient, demonstrating that there is a large margin between the predicted fuel and moderator temperature and accepted safety limits, given a 1650 °C limit for Tristructural Isotropic (TRISO) fuel. These boundary conditions were implemented into a BISON model to demonstrate their use in fuel performance and obtain a brief failure profile of the fuel. The maximum magnitude of the hoop stress on the SiC layer was −12.02 MPa, resulting in a failure probability of 4.90·10−19. Thus, the fuel performance simulations also emphasized the robustness of the TRISO fuel design utilized in the gFHR, as the predictions reveal substantial margin of the TRISO particles relative to temperature limits during the control rod withdrawal. The limiting temperature is expected to be the reactor vessel temperature and the fuel is not expected to be challenged at all by mechanical failure of the SiC layer during these events.

Boron-doped polyhedral graphite catalyzed by h-BN via structural induction for lithium storage

Artificial graphite is extensively used in power lithium-ion batteries for its exceptional stability and high-rate performance. However, the commercial high-temperature graphitization process is conducted at temperatures up to 3000 °C to enhance the degree of graphitization, resulting in significant electricity consumption and lengthy production cycles. This study aimed to lower graphitization temperatures and shorten times by using h-BN as a catalyst. Employing anthracite coal as the precursor and catalyzing with BN at 2800 °C for just 2 h, we achieved a remarkable graphitization degree of 93.3 %, compared to 83.5 % without BN. This indicates BN's effectiveness in accelerating graphite phase formation. Interestingly, the resultant graphite exhibited polyhedral morphology and incorporated boron doping. As edges increased, lithium-ion diffusion pathways and boron doping enhanced stability within the graphite layers, imparting high rate capability and robust cycle performance. The material delivered reversible specific capacities of 369.6 and 226 mA h g−1 at current densities of 0.1 and 3C, and maintained capacity retentions of 95 % and 92 % after 500 cycles at 0.5C and 1C. These results substantiate the potential for large-scale production of artificial graphite from anthracite coal using BN catalysis and underscore its promise as a superior anode material for lithium-ion batteries.

Effect mechanism of phosphorous-containing additives on carbon structure evolution and biochar stability enhancement

The regulation of the pyrolysis process is a key step in increasing the carbon sequestration capacity of biochar. The effect of K3PO4 addition on the yield, chemical composition, characteristic functional groups, macromolecular skeleton, graphite crystallites, and stability of biochar was studied in this paper using two-dimensional infrared correlation spectroscopy (2D-PCIS), X-ray photoelectron spectroscopy, Raman spectrum, and other characterization methods combined with thermal/chemical oxidation analysis. It is discovered that adding K3PO4 may effectively minimize the graphitization temperature range and increase biochar's yield, aromaticity, H/C ratio, and proportion of refractory/recalcitrant organic carbon. The 2D-PCIS and Raman analysis revealed that K3PO4 mostly promoted the dehydrogenation and polycondensation process of the aromatic rings in the char precursor, transforming the amorphous carbon structure of biochar into an ordered turbostratic microcrystalline structure. K3PO4 enhanced biochar stability mostly at medium-high temperatures (350 ~ 750℃) by stimulating the transformation of unstable structures of biochar to stable carbon-containing structures or by inhibiting the interaction of its active sites with oxidants through the mineralization process. A 20% phosphorus addition increased biochar's refractory index (R50) by roughly 11%, and it also boosted biochar's oxidation resistance (H2O2 or K2CrO4) efficiency, reducing carbon oxidation loss by up to 7.31%. However, at higher temperatures (> 750 ℃), the doping of phosphorus atoms into the carbon skeleton degraded the biochar structure's stability. The results of this study suggest that using exogenous phosphorus-containing additives is an efficient way to improve the stability of biochar.Graphical abstract

Utilizing Constant Energy Difference between sp-Peak and C 1s Core Level in Photoelectron Spectra for Unambiguous Identification and Quantification of Diamond Phase in Nanodiamonds.

The modification of nanodiamond (ND) surfaces has significant applications in sensing devices, drug delivery, bioimaging, and tissue engineering. Precise control of the diamond phase composition and bond configurations during ND processing and surface finalization is crucial. In this study, we conducted a comparative analysis of the graphitization process in various types of hydrogenated NDs, considering differences in ND size and quality. We prepared three types of hydrogenated NDs: high-pressure high-temperature NDs (HPHT ND-H; 0-30 nm), conventional detonation nanodiamonds (DND-H; ~5 nm), and size- and nitrogen-reduced hydrogenated nanodiamonds (snr-DND-H; 2-3 nm). The samples underwent annealing in an ultra-high vacuum and sputtering by Ar cluster ion beam (ArCIB). Samples were investigated by in situ X-ray photoelectron spectroscopy (XPS), in situ ultraviolet photoelectron spectroscopy (UPS), and Raman spectroscopy (RS). Our investigation revealed that the graphitization temperature of NDs ranges from 600 °C to 700 °C and depends on the size and crystallinity of the NDs. Smaller DND particles with a high density of defects exhibit a lower graphitization temperature. We revealed a constant energy difference of 271.3 eV between the sp-peak in the valence band spectra (at around 13.7 eV) and the sp3 component in the C 1s core level spectra (at 285.0 eV). The identification of this energy difference helps in calibrating charge shifts and serves the unambiguous identification of the sp3 bond contribution in the C 1s spectra obtained from ND samples. Results were validated through reference measurements on hydrogenated single crystal C(111)-H and highly-ordered pyrolytic graphite (HOPG).

Effects of Graphite Additive Ratio and Temperature on Rheological Properties of Magnetorheological Grease

Effects of Graphite Additive Ratio and Temperature on Rheological Properties of Magnetorheological Grease

Preparation of Ti3SiC2-based diamond composites by Ni–Al assisted self-propagating reaction of Ti–SiC–C system in microwave field

In this paper, the self-propagating reaction of the Ti–SiC–C system for synthesising Ti3SiC2-based diamond composites is ignited by the combustion of Ni–Al alloy powders in a microwave field. The heating curves of Ni–Al-assisted microwave sintering show that the self-propagating reaction could be successfully ignited after heating samples to 685.2 °C in a microwave field for 456 s. This finding indicates that ignition could occur at temperatures below the diamond graphitisation temperature (727 °C). X-ray diffraction analysis indicates that the sintered samples primarily comprise Ti3SiC2, TiC, Ti5Si3 and C. Scanning electron microscopy coupled with energy dispersive spectroscopy observations demonstrates that the diamond grains are tightly bonded with the surrounding matrix and are intact. The best wear ratio of 302.26 was obtained for the Ti3SiC2-bonded diamond composite when the diamond grain size was 140/170 mesh and the molar ratio of Ti, SiC and C was 3:1.1:0.9.

Effect of Impregnation and Graphitization on EDM Performance of Graphite Blocks Using Recycled Graphite Scrap

In the present study, graphite scrap powder from machining of commercial graphite blocks for electrical discharge machining (EDM) applications was recycled as a filler material for manufacturing graphite blocks, and its suitability for use as EDM electrodes was thoroughly assessed. The effects of process parameters applied in EDM electrode manufacturing, including the number of impregnations and graphitization temperatures, on the physical properties of the resulting graphite blocks, were examined. Additionally, EDM performance was evaluated with respect to the above process parameters. In blocks subjected to three impregnation treatments, followed by graphitization at 2200 °C, surface protrusions formed during the EDM process, indicating that the EDM process did not proceed smoothly. On the other hand, in blocks that underwent three impregnation treatments, followed by graphitization at 2800 °C, no surface protrusions were observed, indicating successful EDM operation. This observation further confirms the suitability of these recycled materials for use in EDM electrodes. The graphite block electrodes fabricated using recycled graphite scrap exhibited inferior cyclic stability, with an electrode wear rate of 0.82%, higher than that of a commercial graphite block electrode (0.04%). Nevertheless, using recycled graphite scrap contributes to reducing product costs and CO2 emissions, making the developed graphite electrodes a favorable choice.

Synergistic advancements in sewage-driven microbial fuel cells: novel carbon nanotube cathodes and biomass-derived anodes for efficient renewable energy generation and wastewater treatment

Microbial fuel cells (MFCs) offer a dual solution of generating electrical energy from organic pollutants-laden wastewater while treating it. This study focuses on enhancing MFC performance through innovative electrode design. Three-dimensional (3D) anodes, created from corncobs and mango seeds via controlled graphitization, achieved remarkable power densities. The newly developed electrode configurations were evaluated within sewage wastewater-driven MFCs without the introduction of external microorganisms or prior treatment of the wastewater. At 1,000°C and 1,100°C graphitization temperatures, corncob and mango seed anodes produced 1,963 and 2,171 mW/m2, respectively, nearly 20 times higher than conventional carbon cloth and paper anodes. An advanced cathode composed of an activated carbon-carbon nanotube composite was introduced, rivaling expensive platinum-based cathodes. By optimizing the thermal treatment temperature and carbon nanotube content of the proposed cathode, comparable or superior performance to standard Pt/C commercial cathodes was achieved. Specifically, MFCs assembled with corncob anode with the proposed and standard Pt/C cathodes reached power densities of 1,963.1 and 2,178.6 mW/m2, respectively. Similarly, when utilizing graphitized mango seeds at 1,100°C, power densities of 2,171 and 2,151 mW/m2 were achieved for the new and standard cathodes, respectively. Furthermore, in continuous operation with a flow rate of 2 L/h, impressive chemical oxygen demand (COD) removal rates of 77% and 85% were achieved with corncob and mango seed anodes, respectively. This work highlights the significance of electrode design for enhancing MFC efficiency in electricity generation and wastewater treatment.

Graphitization of anthracite catalyzed by single metal oxides and its enhanced electrical conductivity

ABSTRACT A series of synthetic graphite was fabricated through metal oxide catalytic graphitization using purified anthracite (TYC). The effects of graphitization temperature, catalyst type and its addition methods on structure and properties of graphite products were investigated through the methods of XRD, Raman spectra, SEM, TEM, FTIR and resistivity tester. Increasing graphitization temperature favors the enhancement of order and size of graphite microcrystals, graphitization degree, and conductivity of graphitized products. TiO2 exhibited the best catalytic effects in catalytic graphitization. Compared to directly graphitized TYC at 2800°C (TYC-28), the graphite catalyzed by TiO2 added physically (TYC-28-TiO2) and added chemically (TYC-28-C-TiO2) demonstrated a 13.0 and 16.7% increase in graphitization degree, respectively. Meanwhile, chemical addition method (0.61 × 10−4 Ω·m) outperformed physical addition method (1.21 × 10−4 Ω·m) in improving the electrical conductivity of graphitized products. Moreover, at 2400°C, TYC catalyzed by TiO2 added physically and added chemically presented a graphitization degree of 73.7 and 77.6%, respectively, both exceeding that of TYC-28 (70.7%). Therefore, metallic oxides can enhance the graphitization degree while lowering the required graphitization temperature. This method holds promise for cost-effective and energy-efficient production of high-conductivity graphitized anthracite for batteries, supercapacitors, conductive coatings, and conductive adhesives.

Genesis of the Graphite from the Tugeman Graphite Deposit, Xinjiang, China: Evidence for Carbon Isotope Refining by Fluids Associated with the Ductile Shear Zone

The Altun orogenic belt is situated along the northern boundary of the Tibetan Plateau. In this study, we present an analysis of the ore deposit, mineral composition, and carbon isotope signatures of the Tugeman graphite deposit within the Altun orogenic belt. The graphite in the Tugeman graphite deposit occurs within graphite-bearing schists and marble. Graphite enrichment is observed in the ductile shear zone. The carbon isotope values of graphite range between −18.90‰ and −10.03‰ (with an average value of −12.70‰). These values differ significantly from those observed in organic matter and marine carbonates, suggesting the occurrence of a mixing process involving reduced carbon fluid derived from biological organic material during regional metamorphism as well as a potential influx of oxidized carbon fluid from external sources. In addition, the metamorphic temperature of Tugeman graphite calculated from Raman spectroscopy is between 494 °C and 570 °C, which indicates that the disordered material is transformed from greenschist-amphibolite facies metamorphism to moderate-crystalline graphite. Combining the geological and carbon isotope characteristics of the Tugeman graphite deposit, we argue that the Tugeman graphite deposit is a regional metamorphic graphite deposit of biogenic origin, and during the late stage of metamorphism, it underwent interaction with fluids.

Feasibility for High-Temperature Graphitization of Deformed Meager Coal.

The flattening of nanoscale pores is a crucial step in the process of anthracite graphitization, which primarily occurs due to lithostatic pressure or tectonic stress. Anthracite, a highly metamorphosed form of carbonaceous material, is a primary component of artificial graphite, but its availability is limited in China. Therefore, it is necessary to investigate the graphitization of low metamorphic coal. Note that the pores of deformed coal are substantially compressed, and the evolution of macromolecular structure is accelerated owing to strong tectonic extrusion and shearing action. Herein, the feasibility analysis of coal-based graphite at temperatures of 2200 and 2600 °C was investigated using mylonitized meager coal (YA-M; Ro,max = 2.34%), which exhibits the most intense deformation intensity, and it was compared with undeformed coal (YA-U; Ro,max = 1.87%) from the same coal seam. Results indicate that YA-U primarily consists of cylindrical pores with an average pore diameter of 10 nm, while YA-M exhibits extensive fine bottleneck and parallel plate pores with an average pore size of ∼4 nm. Additionally, interlayer spacing decreases from 0.3592 nm in YA-U to 0.3575 nm in YA-M, while crystallite height increases from 1.9633 nm in YA-U to 2.1424 nm in YA-M. The undeformed coal YA-U exhibits short and disordered aromatic fringes with a localized turbostratic structure that hinders graphitization. In contrast, YA-M exhibits more and longer localized fringe pairs arranged in parallel with improved structural ordering, indicating a favorable environment for graphitization. Ductile deformation narrows the pore diameter distribution, causing deformation pores on the mylonitic granules' surface to close, shrink directionally, collapse, or connect, resulting in obvious flattening characteristics of nanoscale. Based on these results, the graphitization degree of the graphitized products YA-GM-2200 and YA-GM-2600 was 80.23% and 88.37%, respectively, with interlayer spacings of 0.3371 and 0.3364 nm, indicating that these products have entered the semigraphite (medium graphitization) and graphite range, respectively. In contrast, the graphitization degree of YA-GU-2200 and YA-GU-2600 was only 51.16% and 56.98%, respectively, indicating that they have only progressed from anthracite to meta-anthracite (the preliminary graphitization stage). These findings confirm the view that the shear stress generated by the geological age flattens the pores of mylonitized meager coal and optimizes the aromatic lattice arrangement and orientation, facilitating graphitization and lowering the graphitization temperature (from 2800 to 2200 °C). Deformed coal is soft and can be easily crushed into powdered form using the human hand, making it less suitable for transportation. Additionally, owing to the unfavorable separation of minerals and lower hydrocarbon-generating potential, deformed coal application potential and price are consistently lower than those of undeformed coal. However, deformed coal is widely distributed in various coal measures in China, making these research findings valuable in promoting the high value-added utilization of low-rank deformed coal resources and expanding the carbon source of coal-based graphite materials.

Preparation and Characterization of Corn Straw-Based Graphitized Carbon with Ferric Acetylacetonate as Catalyst

Graphitized carbon exhibits exceptional thermal stability, electrical conductivity, corrosion resistance, and various intricate physical and chemical properties. Consequently, it has found extensive applications in diverse fields, such as electrodes, refractory materials, nuclear reactors, and supercapacitors. However, natural graphite is a limited nonrenewable resource, so finding other materials, exploring reliable graphitization methods, and achieving efficient green graphite production as an essential trend in the future is essential. In this paper, with corn straw liquefied product (CSLP) as raw material, ferric acetone catalyst, using carbonization, catalytic graphitization preparation of corn straw based graphitic carbon (CSBGC). When the graphitization temperature was 850 °C and the amount of ferric acetylpropionate (Fe(acac)3) was 7.0 mmol/g, the graphitized carbon showed better graphitization, micro fragmentation structure, and more minor defects, which effectively reduced the graphitization temperature, and the graphitic carbon rate of corn straw (CS) reached 25.2%. This study not only presents a highly efficient approach for synthesizing superior biomass-derived graphite carbon but also introduces usable perspectives on using corn straws.

In situ high-temperature X-Ray diffraction study of tantalum metal

An in-situ thermal behavior study was conducted on the metallic tantalum under two conditions. The experimentation was carried out on tantalum pellets which were heated progressively “underwent reaction and under continuous pumping or under controlled monoxide pressure” in a graphite resistance high temperature X-ray diffractometer up to 2300 K. Through the in-situ study, a thermodynamic analysis showed that this involved the formation of Ta2O, Ta2O5 (low temperature modification) and Ta2C likely to be formed between 293 and 2300 K, in agreement with a reaction mechanism that we established to occur in four stages.

Graphite Slurry Heat Treatment Temperature for Improving the Durability of CNWs Anode Materials of Lithium-Ion Batteries

Graphite Slurry Heat Treatment Temperature for Improving the Durability of CNWs Anode Materials of Lithium-Ion Batteries

Catalytic role of high pressure in the graphitization of amorphous carbon

To accelerate the graphitization transformation efficiency, reduce the transformation threshold of graphitization, and explore the transformation process and catalytic mechanism of amorphous carbon structure under high pressure, we performed rapid graphitization of amorphous carbon materials by a high temperature-high pressure synergistic preparation method. The results show that the high pressure intervention can accelerate the graphitization transformation progress of amorphous carbon materials and reduce the graphitization transition temperature threshold. Especially at 2.8 GPa–1300 °C, the graphitization transformation rate is significantly increased, and the catalytic effect of high pressure is remarkable. The graphitization effect of this method is close to that of the conventional graphitization method at 3000 °C. The high temperature and high pressure synergistic effect reduces the graphitization temperature requirement by 56%, 1 MPa can compensate for the energy loss of 2.15 °C, and the preparation time is substantially reduced. Meanwhile, We summarize the important stages of initial lattice construction, microcrystal growth, and rapid formation of graphitic lattice in the transformation of disordered lattice under the synergistic effect of high temperature and high pressure, clearly showing the different evolutionary features in the process of structural transformation.

Temperature dependence of Cs release during oxidation of Cs-loaded graphite

As one of potential treatments for irradiated graphite (i-graphite) waste, the oxidation method has been attracting more concern due to features of high treating efficiency and significant volume reduction. The release of fission products during oxidation is of great significance for further off-gas decontamination procedures. Focusing on the release behavior of volatile cesium (Cs), Cs-loaded graphite was prepared by impregnation in this work followed by definite distribution and chemical speciation analyzing. Results showed that the increasing temperature and humidity during the oxidation were evidenced to promote the release of Cs compounds, and the chemical speciation of released compounds was prominently dependent on oxidizing temperature. When the oxidation temperature was around 700 °C, Cs2O was predominately released with the morphology of spherical particles. When the oxidation temperature was increased to 900 °C, the predominant releasing composition turned to Cs2CO3 with morphologies of both spherical particles and nanorod-like shapes. The different predominant releasing chemical compositions at different temperatures mainly resulted from the kinetics of graphite oxidization and temperature synergistically. These findings will provide theoretical foundations to the environmental evaluation of i-graphite thermal oxidation.

Advanced boron-doped carbon papers with excellent electrical conductivity and low graphitization temperature for PEM fuel cells

A facile method is proposed in this work to prepare a carbon paper (CP) with outstanding properties by doping boron to catalyze graphitization at lower temperature. Boron was introduced into CP by impregnating carbon fiber preform into a boron/phenolic resin/ethanol solution, and then CP was obtained after the consecutive procedures of hot pressing, carbonization, and graphitization. Morphology, microstructure, composition, and physical properties of the doped and undoped CPs were thoroughly investigated via various techniques to exam the effects of boron concentration and graphitization temperature. Furthermore, the boron doped CP was fabricated into fuel cell gas diffusion layer (GDL) and membrane electrode assembly (MEA) to evaluate its performance through the single cell performance. The findings indicated CP doping with 2 wt% boron could lower the graphitization temperature by at least 200 °C. The B-doped GDL had a higher power density in comparison with the undoped GDLs made in our lab or from the commercial brands.